The present invention relates to a brush holder plate, attached to which are casings accommodating brushes, the brushes extending under spring load in a radial direction towards a central aperture in the brush holder plate. Further, a retaining ring is provided on whose external periphery the brushes abut, the retaining ring being slidable in an axial direction.
The retaining ring serves to facilitate the assembly. Initially, the retaining ring keeps the brushes in retracted positions. As soon as the brush holder plate is slipped on the armature shaft of the motor and the collector secured to it, the collector gradually displaces the retaining ring from its position. As a result of that, the brushes slide from the external periphery of the retaining ring towards the periphery of the collector. This permits an easy and rapid assembly.
German patent application No. 41 05 349 discloses such an arrangement, for example. The holder or prop ring described in the application has a rigid design. During the assembly, the holder is slid by the collector into an accommodating chamber provided in a support of the electric motor housing.
Because it is impossible to conform the outside diameter of the retaining ring exactly to the inside diameter of the accommodating chamber, the retaining ring is likely to have a certain clearance in relation to the accommodating chamber. This means that rattling noise cannot be prevented. Also, wear is caused by the movement of the retaining ring relative to the housing which possibly limits the operability of the electric motor.